Many different types of pumps have been developed over the years for pumping a wide variety of materials. While it has proven relatively easy to develop pumps for use with a wide range of liquid materials having wide viscosity ranges, it has proven more difficult to develop pumps for use with more "exotic" materials. Such exotic materials may include, without limitation, inhomogeneous sludges, cement slurries, paints, paint pigments, or pastes, including toothpastes, peanut butter, mashed potatoes, etc. Non-Newtonian fluids, e.g., fluids in which the shearing stress is not proportional to the rate of shearing deformation, have also proven difficult to pump.
While pumps have been developed that are capable of pumping some types of exotic materials, they are not without their disadvantages. For example, many such pumps utilize rotating members, e.g., impellers, gears, screws, or vanes, which can subject the material being pumped to relatively high shear stresses. Such high shear stresses may break down or otherwise damage certain materials, thus making such pumps unsuitable for use with "shear sensitive" materials. The rotating members of such pumps must also be provided with bearings and seals, which may eventually leak and, in any event, usually require periodic maintenance, particularly of the material being pumped is highly corrosive. The flow rates and discharge pressures of such rotating pumps usually cannot be separately controlled which can pose difficulties in certain applications. Another problem with pumps having rotating members is that they are not well-suited for pumping slurries having relatively large solid particulate matter contained therein.
Diaphragm pumps are another type of pump which may be used to pump certain types of exotic materials. Diaphragm pumps are usually better suited for pumping slurries since they do not require rotating members to move the material. Another advantage of diaphragm pumps is that they tend not to subject the material to excessive shearing stresses, thereby allowing them to be used with certain types of shear sensitive materials. Most diaphragm pumps generally require one or more check valves to ensure that the material being pumped flows in the proper direction. Unfortunately, however, the check valves generally impose limitations on the type of material that may be pumped with diaphragm pumps. Another problem with many diaphragm pumps is that they may include relatively complex mechanical apparatus to move the diaphragms to produce the pumping action. Such mechanical apparatus may require periodic maintenance and may also be prone to failure.
Consequently, a need remains for a pump that can be used effectively with a wide range of materials, including "exotic" materials such as inhomogeneous sludges, cement slurries, paints, paint pigments, or pastes, including toothpastes, peanut butter, mashed potatoes, etc., as well as non-Newtonian fluids. Such a pump should also not subject the material being pumped to excessive shear stresses, therefore allowing the pump to be used with shear sensitive materials. Ideally, such a pump should include a minimum number of moving mechanical components, thereby minimizing maintenance and increasing reliability. Additional advantages could be realized if the flow rate and discharge pressure of such a pump could be independently controlled.